The present disclosure relates to a method for predefining a rotational speed of a drive machine of a drive system comprising at least the drive machine and a hydrostatic drive unit.
The disclosure is described essentially with reference to drive systems which are embodied as (mobile) working machines (for example excavators, mobile cranes, handling equipment), wherein a hydrostatic drive unit is driven by a drive machine, usually an internal combustion engine. The hydrostatic drive unit usually comprises one or more hydraulic pumps which are driven by the drive machine and one or more hydraulic motors which are connected thereto (for rotational movement) and/or hydraulic cylinders (for linear movement) and, if appropriate, valves and the like for actuating the loads.
In the known working machines, a setpoint rotational speed for the internal combustion engine is frequently derived directly from a pedal position or joystick position. In a simple refinement, an idling automatic system is used for this, which system predefines a low idling rotational speed as a setpoint rotational speed in the case of non-activation of the input devices, and predefines a fixed relatively high setpoint working rotational speed in the case of activation of the input devices. The solution is disadvantageous, in particular, with respect to the fuel consumption since the working rotational speed is not adapted to the actual power requirement.
In addition it is possible to predefine a variable setpoint working rotational speed as a function of the activation of the input devices. However, this proportional approach is also disadvantageous with respect to the response behavior and fuel consumption since the efficiency of the turbo-charged internal combustion engines which are generally used and which essentially also determines the response behavior of a working machine at the overall system level depends not only on the rotational speed but also, for example, on the current charge pressure.
It is therefore desirable to predefine a rotational speed for a drive machine of a drive system in such a way that the consumption and, in particular, response behavior are improved.